This invention relates to a process for manufacturing a lightweight, axle, useful for automotive vehicles and particularly for trucks. This manufacturing process produces axles whose wall thicknesses, in cross-section, vary so that the wall thicknesses are greater where greater load absorption is required and reduced where a lesser load is to be absorbed with the result that the weight of the axle can be reduced without reducing its strength.
Axles have been manufactured in the past by a cold forming process which involves extruding a tubular blank through the constricted die throat of a die, utilizing a punch for pushing the blank through the die throat. The punch has been formed with an annular ram surface for engaging the trailing end of the blank and pushing it towards and through the die throat. In addition, the punches have been formed with forwardly oriented extensions which are positioned within the die throat to provide annular spaces through which the blank is extruded. By appropriately manipulating the extensions which are of different diameters, portions of the wall thickness of the extruded tube can be made thicker while other portions can be made thinner. In cross-section, however, the wall thicknesses are uniform.
Examples of this type of process are disclosed in U.S. Pat. No. 4,435,972 issued Mar. 13, 1984 to Joseph A. Simon for a "Process for Forming Integral Spindle-Axle Tubes". A further example of such type process is disclosed in U.S. Pat. No. 5,105,644 issued Apr. 21, 1992 to Joseph A. Simon for a "Light Weight Drive Shaft". Other disclosures of this type of process are found in U.S. Pat. No. 5,241,848 issued Sep. 7, 1993 to Joseph A. Simon for a "Light Weight Drive Shaft" and U.S. Pat. No. 5,388,322 issued Feb. 14, 1995, to Joseph A. Simon for a "Method for Making a Shatterproof Air Bag Inflator Pressure Vessel".
The present invention is concerned with adapting or utilizing a process of the previously mentioned type, but wherein the process is changed to produce tube interior wall portions, which are generally elliptical, rather than circular, in cross-sectional shape. Thus, the cross-sectional shape of such tube portions are varied or non-uniform in thickness. The tube can be oriented, when it is used, in a way that accommodates applied loads while nevertheless reducing the metal and, therefore, the weight of the tube in areas which are not subject to high loads.